Inclusion Complex of α-Cyclodextrin with Poly(ethylene glycol) Brush

Polyurethane-Type Poly[3]rotaxanes Synthesized from Cyclodextrin-Based [3]Rotaxane Diol and Diisocyanates

Synthesis of polyurethane-type poly[3]rotaxanes is achieved by polyaddition between a cyclodextrin (CD)-based [3]rotaxane diol and various diisocyanate species, which provide a more defined structure compared to conventional polyrotaxane syntheses. In this study, hydroxyl groups on CDs of [3]rotaxane diol are initially acetylated, and deprotected after the polyaddition to introduce polyurethane backbone structure into polyrotaxane framework. Despite a relatively complicated chemical structure, [3]rotaxane diol monomer is successfully synthesized in a high yield (overall 67%) without any taxing purification process, which is beneficial for practical applications. The polymerization itself proceeds well under a standard polyaddition reaction condition to afford corresponding polyurethanes around 80% yield with Mn > 30 kDa. The poly[3]rotaxanes show different aggregation behavior or optical properties, whether or not acetyl groups are present, and are analyzed by XRD, SEM, and fluorescence measurements.

Aggregation Behavior of Cyclodextrin-Based [3]Rotaxanes

The aggregation of a cyclodextrin (CD)-based [3]rotaxane has been observed and analyzed in detail for the first time in this work. Although the hexagonal packing aggregation of CD-based polyrotaxane is a well known phenomenon, corresponding studies in terms of rotaxanes without any polymer structure have not been conducted so far, probably owing to the difficulty of the molecular design. We synthesized a series of [3]rotaxane species by using a urea-end-capping method and evaluated their aggregation behavior by XRD and SEM measurements. [3]Rotaxane species containing native CD rings showed clear signals assigned to the hexagonal packing by XRD measurement as did polyrotaxane; this proved their aggregation capability. Because the corresponding per-acetylated derivatives did not show this aggregation behavior, the driving force of this aggregation was suggested to be hydrogen bond formation among CD units. The effect of axle end structures and partial acetylation of CDs were also studied.

Assembly of Supramolecular Nanoplatelets with Tailorable Geometrical Shapes and Dimensions

The craving for controllable assembly of geometrical nanostructures from artificial building motifs, which is routinely achieved in naturally occurring systems, has been a perpetual and outstanding challenge in the field of chemistry and materials science. In particular, the assembly of nanostructures with different geometries and controllable dimensions is crucial for their functionalities and is usually achieved with distinct assembling subunits via convoluted assembly strategies. Herein, we report that with the same building subunits of α-cyclodextrin (α-CD)/block copolymer inclusion complex (IC), geometrical nanoplatelets with hexagonal, square, and circular shapes could be produced by simply controlling the solvent conditions via one-step assembly procedure, driven by the crystallization of IC. Interestingly, these nanoplatelets with different shapes shared the same crystalline lattice and could therefore be interconverted to each other by merely tuning the solvent compositions. Moreover, the dimensions of these platelets could be decently controlled by tuning the overall concentrations.

High-yield one-pot synthesis of polyrotaxanes with tunable well-defined threading ratios over a wide range

In this work, we report a high-yield one-pot synthesis of polyrotaxane (PR), composed of (2-hydroxypropyl)-α-cyclodextrin (hpCD) and polyethylene glycol (PEG), with well-defined hpCD threading ratios controllable across a wide range from 0.64% to 10%. In hpCD/PEG aqueous solutions, hpCDs are well dispersed and threaded spontaneously into hpCDs to form a pseudo-PR (pPR) structure. The homogeneous dispersion of hpCDs results in a well-defined threading ratio of hpCDs on PEG, which is suggested by the fact that the dispersity of the molecular weight distribution of PR is almost the same as that of pure PEG. The well-defined hpCD threading ratio of the PRs can be controlled over a wide range by tuning the hpCD concentration in the pPR solutions.

In this work, we report a high-yield one-pot synthesis of polyrotaxane (PR), composed of (2-hydroxypropyl)-α-cyclodextrin (hpCD) and polyethylene glycol (PEG), with well-defined hpCD threading ratios controllable across a wide range from 0.64% to 10%.

Modification of a Polymer Surface by Partial Swelling Using Nonsolvents

Surface modification without changing the physical properties in the bulk is of pivotal importance for the development of polymers as devices. We recently proposed a simple surface functionalization method for polymer films by partial swelling using a nonsolvent and demonstrated the incorporation of poly(2-methoxyethyl acrylate) (PMEA), which has an excellent antibiofouling ability, only into the outermost region of a poly(methyl methacrylate) (PMMA) film. We here extend this technology to another versatile polymer, polystyrene (PS). In this case, PS and PMEA have different solubility parameters making it difficult to select a suitable solvent, which is a nonsolvent for PS and a good solvent for PMEA, unlike the combination of PMMA with PMEA. Thus, such a solvent was first sought by examining the swelling behavior of PS films in contact with various alcohols. Once a mixed solvent of methanol/1-butanol (50/50 (v/v)) was chosen, PMEA chains could be successfully incorporated at the outermost region of the PS film. Atomic force microscopy in conjunction with neutron reflectivity revealed that chains of PMEA incorporated in the PS surface region were well swollen in water. This leads to an excellent ability to suppress the adhesion of platelets on the PS film.

Direct enhancement of intercomponent interactions in polyrotaxane and its pronounced effects on glass state properties

Strong interactions between the host cyclodextrin and the threading guest polymer were introduced by selective modifications to the polymer of a polybutadine-based polyrotaxane. The changes in the intercomponent interactions influenced the mobility of the threading polymer that was confined in the glassy host framework, resulting in different mechanical properties.

PEG-α-CD/AM/liposome @amoxicillin double network hydrogel wound dressing-Multiple barriers for long-term drug release

Wound infection and poor wound healing are the major challenges of wound treatment. Antibiotic drug treatment is the effective way to inhibit wound infection. It is necessary to achieve sustained release of antibiotics to get a longer treatment for wound infection. The double network hydrogels based on liposome, polyethylene glycol (PEG), α- cyclodextrin (α-CD) and acrylamide (AM) were developed, in which liposome acts as amoxicillin repository. Because the drug would release from the multiple barriers including two cavities of liposome and α-CD, as well as polyethylene glycol -α- cyclodextrin/acrylamide (PEG-CD/AM) double network, the PEG-α-CD/AM/liposome @amoxicillin double network hydrogels could achieve sustained drug release. The drug release assay showed that the dressing could release amoxicillin continuously until 12 days, than that of 8th day for single-network hydrogel releasing. The antibacterial ratio of the hydrogel could reach above 80%. What's more, the hydrogels present adjustable mechanical strength by changing the ratio of the components. The swelling ratio proved that the hydrogel had potential ability to absorb wound exudates. The cytotoxicity test of the hydrogels demonstrated excellent biocompatibility. These results indicated that this study can provide a new thought for antibacterial wound dressing and has a broad application prospect.

Precise control of cyclodextrin-based pseudo-polyrotaxane lamellar structure via axis polymer composition

Self-assembly of cyclodextrin (CD) with guest polymers has attracted much attention owing to its biocompatibility and accessibility. In this study, we investigate the composition effect of poly(ethylene oxide)m-b-poly(propylene oxide)n-b-poly(ethylene oxide)m (EOmPOnEOm) triblock copolymers on lamellar or plate structures formed by complexation with β-CD. EO5PO29EO5, EO14PO29EO14, and EO75PO29EO75 show periodic lamellar morphology consisting of single-crystalline pseudo-polyrotaxane (PPR) nanosheets with a thickness equal to the central PO length. This is because β-CDs selectively cover the PO component and cause the microphase separation between β-CD and EO layers. The thickness of the EO layers increases linearly with increasing number of EO units, which suggests that the EO chains are constrained into virtual cylinders with the diameter of the β-CD. This means that we can precisely control the thickness of both the crystal (β-CD and PO) and the amorphous (EO) layers in the lamellar structure. In contrast, EO2PO29EO2 forms a thin plate structure, where not only PO but also EO chains are covered with β-CD. Furthermore, the length of the central PO component is necessary to form the lamellar structure with the phase separation between the β-CD and EO layers. These findings provide a more fundamental understanding to enhance the variety and applicability of CD-based self-assembled materials.

Inclusion Complexation between α-Cyclodextrin and Oligo(ethylene glycol) Methyl Ether Methacrylate

The preparation of inclusion complexes based on α-cyclodextrin (α-CD) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) was investigated aiming to reveal complexation particularities and thermodynamic and kinetic aspects as a function of the oligomer architecture. Small-angle X-ray scattering and isothermal titration calorimetry measurements revealed that oligomer molecular weight controls both the kinetics and thermodynamics of inclusion. Unlike linear ethylene glycol polymers, OEGMA groups possess a methacrylate group, which seems to act as a stopper, affecting their mode of complexation. Nuclear magnetic resonance spectra and relaxation measurements support the fact that methacrylate groups lie outside the α-CD ring and that a full sequential complexation of the oligomer ethylene oxide groups is not observed. These results allied to the temperature sensitivity of these oligomers and enable possible routes for chemical modifications and design of new stimuli-responsive materials.

Facile preparation of one-dimensional nanostructures through polymerization-induced self-assembly mediated by host–guest interaction

A RAFT aqueous dispersion polymerization of ferrocenylmethyl acrylate mediated by host–guest interaction was investigated and a series of peculiar one-dimensional morphologies can be readily obtained.

Nanoparticles decorated with folate based on a site-selective αCD-rotaxanated PEG-b-PCL copolymer for targeted cancer therapy

NPs fabricated from a mixture of PEG-b-PCL and selectively rotaxanated Fol-PEG(αCD)-PCL showed internalisation in KB cells through an active targeting mechanism.

α-Cyclodextrin-Based Polypseudorotaxane Hydrogels

Supramolecular hydrogels that are based on inclusion complexes between α-cyclodextrin and (co)polymers have gained significant attention over the last decade. They are formed via dynamic noncovalent bonds, such as host-guest interactions and hydrogen bonds, between various building blocks. In contrast to typical chemical crosslinking (covalent linkages), supramolecular crosslinking is a type of physical interaction that is characterized by great flexibility and it can be used with ease to create a variety of "smart" hydrogels. Supramolecular hydrogels based on the self-assembly of polypseudorotaxanes formed by a polymer chain "guest" and α-cyclodextrin "host" are promising materials for a wide range of applications. α-cyclodextrin-based polypseudorotaxane hydrogels are an attractive platform for engineering novel functional materials due to their excellent biocompatibility, thixotropic nature, and reversible and stimuli-responsiveness properties. The aim of this review is to provide an overview of the current progress in the chemistry and methods of designing and creating α-cyclodextrin-based supramolecular polypseudorotaxane hydrogels. In the described systems, the guests are (co)polymer chains with various architectures or polymeric nanoparticles. The potential applications of such supramolecular hydrogels are also described.

Supramolecular Fluorine Magnetic Resonance Spectroscopy Probe Polymer Based on Passerini Bifunctional Monomer

A water-soluble fluorine magnetic resonance spectroscopy host-guest probe, P(HPA-co-AdamCF₃A), was successfully constructed from the facile synthesis of a bifunctional monomer via a quantitative Passerini reaction. Supramolecular complexation with (2-hydroxypropyl)-β-cyclodextrin promoted a change in the chemical environment, leading to modulation of both the relaxation properties as well as chemical shift of the fluorine moieties. This change was used to probe the supramolecular interaction by ¹⁹F MRI spectroscopy and give insight into fluorine probe formulation. This work provides a fundamental basis for an ¹⁹F MR imaging tracer capable of assessing host-guest inclusion and a potential model to follow the fate of a drug delivery system in vivo.

Autonomously isolated pseudo-polyrotaxane nanosheets fabricated via hierarchically ordered supramolecular self-assembly

Autonomously isolated PPR nanosheets are fabricated via complexation between β-CD and a carboxyl-terminated poloxamer and the structural coloration was exhibited.

Supramolecular Hybrid Structures and Gels from Host-Guest Interactions between α-Cyclodextrin and PEGylated Organosilica Nanoparticles

Polypseudorotaxanes are polymer chains threaded by molecular rings that are free to unthread; these "pearl-necklace" can self-assemble further, leading to higher-order supramolecular structures with interesting functionalities. In this work, the complexation between α-cyclodextrin (α-CD), a cyclic oligosaccharide of glucopyranose units, and poly(ethylene glycol) (PEG) grafted to silica nanoparticles was studied. The threading of α-CD onto the polymeric chains leads to their aggregation into bundles, followed by either the precipitation of the inclusion complex or the formation of a gel phase, in which silica nanoparticles are incorporated. The kinetics of threading, followed by turbidimetry, revealed a dependence of the rate of complexation on the following parameters: the concentration of α-CD, temperature, PEG length (750, 4000, and 5000 g mol^-1), whether the polymer is grafted or free in solution, and the density of grafting. Complexation is slower, and temperature has a higher impact on PEG grafted on silica nanoparticles compared to PEG free in solution. Thermodynamic parameters extracted from the transition-state theory showed that inclusion complex formation is favored with grafted PEG compared to free PEG and establishes a ratio of complexation of five to six ethylene oxide units per cyclodextrin. The complexation yields, determined by gravimetry, revealed that much higher yields are obtained with longer chains and higher grafting density. Thermogravimetric analysis and Fourier transform infrared spectroscopy on the inclusion complex corroborate the number of macrocycles threaded on the chains. A sol-gel transition was observed with the longer PEG chain (5k) at specific mixing ratios; oscillatory shear rheology measurements confirmed a highly solid-like behavior, with an elastic modulus G' of up to 25 kPa, higher than that in the absence of silica. These results thus provide the key parameters dictating inclusion complex formation between cyclodextrin and PEG covalently attached to colloidal silica and demonstrate a facile route toward soft nanoparticle gels based on host-guest interactions.

Polyrotaxane Brushes Dynamically Formed at a Water/Elastomer Interface

Dense polymer brushes with closely packed rotaxane structures were formed at the interface of water and a styrene-butadiene elastomer by spontaneous segregation of an amphiphilic polyrotaxane (PR), a mechanically interlocked polymer consisting of hydrophobic polybutadiene threading through multiple hydrophilic γ-cyclodextrin (γ-CD) derivatives. Segregation of PR at the water/elastomer interface was suggested by X-ray photoelectron spectroscopy. The polymer brush structure at the water interface was investigated using neutron reflectometry. Brush structures were found to depend on the number of CDs on the PRs; the PR with a small number of CDs formed a thinner and homogeneous brush, whereas the PR with a higher number of CDs formed a thicker and less-ordered brush. These PR-brushes showed protein repulsion, resulting from the surface-hydrated brush layer preventing direct contact of proteins.

Branched polyrotaxane hydrogels consisting of alpha-cyclodextrin and low-molecular-weight four-arm polyethylene glycol and the utility of their thixotropic property for controlled drug release

In this work, we developed a new class of branched polyrotaxane hydrogel made of 4-arm polyethylene glycol (4-PEG) and α-cyclodextrin (α-CD) using supramolecular host-guest interactions as a cross-linking strategy. Because of the dynamic nature of the non-covalent host-guest cross-linking, the resulting supramolecular α-CD/4-PEG hydrogels show thixotropic behavior and undergo a reversible gel-sol transition in response to shear stress change. We loaded the antiglaucoma drug brimonidine into the α-CD/4-PEG gel and found the drug release kinetics was controlled by shear stress. This thixotropic shear thinning property makes the supramolecular hydrogels highly attractive in drug delivery applications and suitable for preparation of injectable drug formulations.

Design of a Well-Defined Polyrotaxane Structure on a Glassy Polymer Surface

The polymer dynamics at the water interface play a crucial role in the manifestation of biorelated functions. One of the strategies for this is to form inclusion complexes of polymer chains with cyclic compounds. However, such an idea has been limited to bulk materials so far. Here we propose a preparation pathway for a polyrotaxane structure composed of poly(ethylene oxide) (PEO) and α-cyclodextrin (CD) at the outermost surface of a glassy poly(methyl methacrylate) film on the basis of the combination of a click reaction and the Langmuir-Blodgett method. The chain motion of PEO at the water interface could be regulated by threading of CD molecules on PEO and thereby the biological responses such as protein adsorption and platelet adhesion altered depending on the extent of complexation.

Quantitative Analysis of Polymer Brush Formation Kinetics Using Quartz Crystal Microbalance: Viscoelasticity of Polymer Brush

Polymer brush formation kinetics was measured by quartz crystal microbalance (QCM). In the QCM measurement anomalous complex frequency shift as a function of graft density was observed: dissipation rate shift ΔΓ first increased, showed a peak, and then decreased despite the graft density of the polymer brush was increasing monotonically. We calculated the shear modulus of the brush layer from the measured complex frequency shift and revealed that the peak of ΔΓ described the crossover from a viscous brush layer to elastic brush layer. The crossover for the poly(ethylene glycol) with a molecular weight of 2000 occurs at around the characteristic graft density of 0.17 chains/nm² which was revealed from the structure analysis by surface plasmon resonance (SPR) and neutron reflectivity (NR).

On the formation of inclusion complexes at the solid/liquid interface of anchored temperature-responsive PNIPAAM diblock copolymers with γ-cyclodextrin

The thermal responsive behavior of adsorbed layers of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAAM) and poly((3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA(+)) with γ-cyclodextrin (γ-CD) at the solid/liquid interface has been investigated using three in situ techniques: null ellipsometry, quartz-crystal microbalance with dissipation monitoring, and neutron reflectometry. The measurements provided information about the adsorbed amounts, the layer thickness, hydration and viscoelastic properties, and the interfacial structure and composition. The copolymers adsorb to silica with the cationic PAMPTMA(+) blocks sitting as anchors in a flat conformation and the PNIPAAM chains extending into the solution. The copolymer system alone exhibits reversible collapse above the lower critical solution temperature of PNIPAAM. The addition of γ-CD to pre-adsorbed copolymer layers results in a highly extended conformation as well as some loss of copolymer from the surface, which we discuss in terms of the formation of surface-invoked lateral steric repulsion of formed inclusion complexes.